If a Tree Falls in a Forest and No One Hears It, Does It Make a Noise?

The answer to this famous riddle depends on how we define sound. One way is to define sound as something that is heard. According to this definition, the tree makes no sound because no one hears it. We can also define sound as vibrations produced by an object.

According to this definition, the tree makes sound because it produces vibrations, or sound waves, when it crashes. Most scientists use the second definition. This definition describes events that occur in nature, rather than the act of hearing these events. What do you think?

Can something exist without being perceived? — e.g. “is sound only sound if a person hears it?” The most immediate philosophical topic that the riddle introduces involves the existence of the tree (and the sound it produces) outside of human perception. If no one is around to see, hear, touch or smell the tree, how could it be said to exist? What is it to say that it exists when such an existence is unknown? Of course, from a scientific viewpoint, it exists. It is human beings that are able to perceive it.

George Berkeley in the 18th century developed subjective idealism, a metaphysical theory to respond to these questions, coined famously as “to be is to be perceived”. Today meta-physicists are split. According to substance theory, a substance is distinct from its properties, while according to bundle theory, an object is merely its sense data.

The definition of sound, simplified, is a hearable noise. The tree will make a sound, even if nobody heard it. The definition states that sound is a hearable noise. So the tree could have been heard, though nobody was around to do so.

Content for this question contributed by Neal Allen, resident of Holyoke, Hampden County, Massachusetts, USA